The design of voltage controlled current source (VCCS) for single frequency electrical impedance tomography (EIT)

摘要

Electrical Impedance Tomography (EIT) is an imaging technique for mapping the conductivity distribution of an object. One of the most significant circuit blocks in the EIT system is Voltage Controlled Current Source (VCCS) circuit. The VCCS should be able to supply a current ranging from 0.5 to 5 mA at 10 kHz-1 MHz and should be adequate to support the load at the range of 100 Ohm-10 kOhm. The main purpose of this study is to design the VCCS with a constant current of 1 mA at 20 kHz. We designed four types of VCCS by using two types of voltage-controlled oscillator (VCO) circuits, two types of voltage to current converter (VCC) circuits, and a fourth order Butterworth Bandpass Filter (BPF) circuit (Sallen-Key topology). The VCO circuit was designed with two types of Integrated Circuits (IC) which are XR2206 (VCO 1) and AD9850 (VCO 2), whereas the VCC circuit was fabricated based on Enhanced Howland (EH) circuit (VCC 1) and Triple Op-Amp circuit (TOA) (VCC 2). The results show that VCCS 4 which was designed with the combination of VCO 2, VCC 2, and BPF gave the best performance compared to the three other types of VCCS circuit. The VCCS 4 is capable of delivering a constant current for 1 mA at 20 kHz with a load value of up to 3.72 kOhm. However, the four VCCS types that have been designed could be used as a current source in the EIT system for a single frequency.